There has heretofore been a head-up display unit (refer to FIG. 6) adapted to display a virtual image V by projecting display light L from a display unit 2 onto a windshield 1 of a vehicle. The display unit 2 houses (refer to FIG. 7) therein a display 3, such as a fluorescent display tube, a reflecting mirror 4 adapted to reflect display light L emitted by this display 3, and a stepping motor 5 for turning this reflecting mirror 4. A turning shaft of the stepping motor 5 is mounted with a gear 7, which is meshed with a gear portion 9 fixed to a retainer member 8 retaining the reflecting mirror 4.
A driver can regulate a direction in which the display light L is projected onto the windshield 1 by setting an angular position of the reflecting mirror 4 in a range of angle (for example, 6°) between an upper limit position and a lower limit position by his operation of a pushbutton switch (not shown). For example, when an angular position of the reflecting mirror 4 is set to a position in the vicinity of a lower limit position, the reflected display light can be advanced so as to enter the eyes of a driver D1 of a higher visual point. When an angular position of the reflecting mirror 4 is set to a position in the vicinity of a higher limit position, the reflected display light can be advanced so as to enter the eyes of a driver D2 of a lower visual point. In order to prevent a drawing from becoming complicated, the angular range between the upper limit position and lower limit position is shown on an enlarged scale in FIG. 8.
Even when an ignition switch is turned off in such a head-up display unit, the angular position of the reflecting member is maintained at a level set by the driver. Therefore, the sunlight is reflected on the reflecting mirror 4, and the display 3 is irradiated with the reflected sunlight to cause the display 3 to be deteriorated. There is a head-up display unit which is disclosed in JP-A-2002-137189 as a head-up display unit solving such a problem, and which is adapted to change an angular position of a reflecting mirror 4 so that the sunlight does not reflect toward a display 3 when an ignition switch is turned off.
It is desirable that, when the ignition switch is turned off in the head-up display unit disclosed in the above-mentioned publication, the angular position of the reflecting mirror 4 be returned to a predetermined original position. However, an angular movement of the reflecting mirror 4 is made usually for the purpose of regulating the direction in which the display light L is projected onto a windshield 1 by operating the above-mentioned pushbutton switch, so that the angular position of the reflecting mirror is moved at a comparatively low speed. Therefore, this head-up display unit had inconveniences of requiring time between the turning on of an ignition switch and the attainment of the original position of the reflecting mirror 4 during its returning movement thereto.
The present invention has been made in view of this problem, and aims at providing a display unit for vehicles which is capable of angularly moving such a reflecting member as is mentioned above to an original position in a comparatively short period of time even in the case where the reflecting member is angularly moved to a predetermined original position when an ignition switch is turned on.